The invention generally relates to wafer cassette holding mechanisms in semiconductor manufacturing equipments. More particularly, the invention relates to an apparatus for calibrating the position of the support platform of a wafer cassette holder with respect to a robot blade so as to achieve alignment to the robot blade of cassettes placed upon the support platform.
Modern semiconductor manufacturing equipments use automated wafer transport systems in order to reduce human handling of wafers and therefore decrease the risks of particle contamination of the wafers. In such semiconductor processing equipments, wafers are generally stored in cassettes having parallel, stacked slots each of which is receptive to a single, often horizontally oriented, wafer. Typically, a cassette is placed on a cassette holder of the wafer processing equipment and the blade of a robot arm extends to slots in the cassette for loading or unloading wafers from the cassette. Given the high sensibility and fragility of the wafers to contacts, such a robot arm must be very accurate in loading and unloading wafers from a cassette, so as to avoid any rubbing or shocks that could damage the wafers. In this end, the cassette placed on a cassette holder must be accurately aligned to the blade of the robot arm. Typically, a cassette holder includes an adjustment means such as screws, for tuning the level position of the support platform. By using this adjustment means, a human operator can adjust the height and the parallelism of a cassette placed on the support platform with respect to the blade of the robot arm. When the adjustment of the cassette alignment is complete, the level position of the support platform is considered calibrated. However, this adjustment procedure suffers from the problem that it is subject to human errors as the cassette alignment with regard to the blade is visually evaluated. Moreover, the accuracy of the cassette alignment is variable depending on the person in charge of the calibration, and the adjustment is not repeatable as no two cassette alignments can be made identical by one person. Furthermore, errors in appreciation may sometimes result in scratched wafer, increased contamination, and time loss.
A main object of the invention is therefore to provide a wafer cassette holder calibration apparatus that enables a human operator to calibrate the alignment of a wafer cassette holder with respect to the blade of a robot arm, thereby achieving a highly accurate and repeatable adjustment.
In brief, in accordance with the appended set of claims, this object is achieved by providing an APPARATUS FOR CALIBRATING the position of the support platform of a wafer cassette holder with respect to a robot blade. The apparatus comprises a housing including an open front portion which permits the convenient extending of the robot blade into the housing when the apparatus is placed on the support platform. The housing further comprising detecting and measuring means for detecting the presence of a wafer held by the extended robot blade, and measuring the spacing between the detecting and measuring means and the wafer; and a display panel coupled to the detecting and measuring means for displaying spacing information which indicates to a user the moment when the spacing between the wafer and the detecting and measuring means reaches at least one predetermined spacing value including a desired spacing value. That way, when the apparatus is placed on the support platform with the robot blade holding a wafer positioned underneath the detecting and measuring means, the calibration of the position of the wafer cassette holder is carried out by adjusting the position of the support platform so as to reach the desired spacing value. This desired spacing value is typically specified by the cassettes manufacturer.
More specifically, the detecting and measuring means of the calibration apparatus comprises a sensor board which includes a plurality of sensors, and an electronic circuit board which includes electronic circuitry coupled to the first plurality of sensors for processing first electrical signals issued by the plurality of sensors and providing to the display panel second electrical signals indicative of the spacing between each of the sensors and the wafer, upon which the spacing information can be displayed.
In a preferred embodiment of the invention, the sensor board comprises three capacitive sensors, one of which being positioned at the front middle portion of the sensor board and the other two being positioned laterally at opposite sides of the sensor board. The apparatus of the invention is advantageously mounted into a standard wafer cassette with the sensor board mounted substantially parallel to the wafer slots of the wafer cassette, and the display panel being mounted at the back side of the cassette. This contributes to render the calibration apparatus particularly easy to carry and transport.
Still in a preferred embodiment, the display panel of the calibration apparatus of the invention includes a plurality of light-emitting diodes of different colours, whereby an user knows that the desired spacing value is reached for each one of the sensors when a diode of a same predetermined colour is activated for each of the sensors. This makes the display panel particularly convenient and simple for determining that the calibration is complete, without any risk of erroneous interpretation of the information displayed. The display panel advantageously allows to detect a robot blade twist.
Still in accordance with a preferred embodiment of the invention, the display panel includes additional display means coupled to additional sensors in the sensor board through additional electronic circuitry in the electronic circuit board, in order to enable an user to perform robot blade droop measurement, and/or wafer centering measurement, and/or robot blade extension limit measurement.
Still other features of the invention are set out in the dependent claims.
In summary, besides being an efficient and reliable tool for CALIBRATING THE ALIGNMENT OF A WAFER CASSETTE HOLDER TO A ROBOT BLADE, the calibration apparatus of the invention is easy to use, in particular thanks to its advantageous display panel which is also not subject to misinterpretation of the information displayed upon which the adjustment is controlled. Furthermore, the calibration apparatus of the invention is easy to carry and transport, in particular when it is mounted into a standard wafer cassette. It is also technically simple, in particular it does not require a computer console, thus its manufacturing is cost effective.